This invention relates to saw blade sharpening machines, and particularly to such machines utilized to sharpen circular saw blades.
Imperfections, such as blade eccentricity, variable tooth spacing, and variable tooth shape and size are common both in new blades and used blades that have been ground on inadequate machinery or filed by hand. The cost of accurate, semi-automatic sharpening machines for circular saw blades is ordinarily prohibitive to that portion of the market that makes use of circular saw blades. Therefore, when it is desired to resharpen such a blade, the owner must take it to a specialized shop where the blade is sharpened by a complex and extremely expensive piece of machinery. The other recourse for the user is to sharpen the saw blade by hand. This procedure is almost always detrimental to the cutting efficiency of the saw blade since it is nearly impossible for a blade to be precisely sharpened utilizing only hand tools. In fact, continued hand sharpening causes blade eccentricity which, in turn, can eventually cause bearing damage and excessive wear on the arbor of the saw on which the blade is mounted.
Continuous filing of circular saw blades causes the tooth periphery to become out of round. A process called "jointing" is utilized to return the blade periphery to a balanced circular configuration. This process produces "flats" or "brights" on each tooth point on the saw. These "flats" are produced by mounting the saw blade on an arbor and holding an abrasive surface against the saw blade as it is rotated. The surface is held rigidly against movement with the out-of-round saw blade. The result is that the "flats" are formed, replacing the points of all or nearly all the teeth on the saw blade. For filing purposes these "flats" are utilized to determine depth of cut necessary to bring the saw blade back to its true circular shape. The present device eliminated the necessity of jointing a saw blade separately from the grinding operation by precisely locating the depth and spacing of each tooth during the grinding operation.
Another step in the process of sharpening circular saws is called "gumming." "Gumming" may be defined as the deepening of the gullets between adjacent teeth for more efficient removal of sawdust from the kerf. Deep gullets also facilitate filing by spacing adjacent teeth apart a distance sufficient to allow clearance of a file or grinding disc. Often gullets are formed at an angle that is critical to the operation of the saw blade. The gullet is tangential to the "face" of one tooth and the "tooth back" of an adjacent tooth. The front face of the tooth forms a positive or negative "rake" angle. In some grinding operations, the gullet and rake angle are ground simultaneously since the grinding disc is predressed to the desired configuration, and the saw blade is held at a prescribed angle relative to the plane of the grinding disc.
It is also often required to produce one or more beveled surfaces along circular saw blade teeth. A bevel is any tooth surface that is angularly offset from a surface that is normally perpendicular to the planar sides of a saw blade. Often, bevels on successive teeth are set at equal but opposite angles to the plane of the blade sides.
Ordinarily, the planar surfaces of the saw blades are held perpendicular to the grinding surface. Grinding bevels is accomplished by holding the saw blade with its planar sides at a prescribed angle relative to the surface of a grinding disc. In most grinding machines, bevels are formed by angulating the blade surface and subsequently grinding all the prescribed bevels for a particular angle, then the blade is shifted to another angle so the remaining opposite bevels may be ground.
Circular saw blades come in many different sizes, utilizing many different numbers of teeth, and differing teeth configurations. Rip saws generally have all teeth of the same configuration. Cross-cut saws may also have all teeth identical. However, almost all combination type saws that are utilized both for cross-cut and ripping purposes have sets of teeth spaced about the saw periphery and separated by deep gullets. Each set of teeth includes a plurality of shortened "spurs" with a large "raker" tooth at the forward edge of the group. Sharpening of a combination blade is ordinarily more difficult than sharpening of a standard rip saw blade or a cross-cut blade that has all teeth identical. The "spurs" and "rakers" must be filed or ground separately since the angles are seldom the same for both the raker and spur teeth.
It has also been found that automatic grinding machines are insensitive to grinding pressures that may result in excessive blade heat during the sharpening process. Excessive heat removes blade "tension" and will often cause a blade to wobble when rotating at relatively high RPM on a saw arbor. A manually controllable device allows for "light-touch" grinding with several passes possibly being made over an area in order to bring it to the proper condition without causing excessive blade heat.
It is desirable to provide some form of apparatus whereby circular saw blades may be precisely sharpened and reshaped or "trued" without requiring purchase of an extremely expensive and complex piece of machinery. It is also desirable to offer such a machine that is simple in design and relatively easy to operate.
U.S. Pat. No. 3,457,809 to Martin Bowerman discloses a saw blade grinder for sharpening teeth of all types of circular saws. The arbor and mounting base for this machine are movable from a position where the blade may be sharpened, to another position where the individual blade teeth may be "set." The grinding wheel of this device must be dressed to the configuration of the particular teeth to be sharpened. In addition, the teeth of the saw blade are used as a spacing index to present each successive tooth to the grinding operation. If the gullet depth is correct and the blade has been jointed, it is possible to obtain a serviceable and relatively efficiently sharpened blade from this device.
U.S. Pat. No. 545,064, granted to Fleck, describes a saw sharpening machine that utilizes a fixed arbor for a saw blade and a relatively movable grinding disc to effect the grinding of the blade. The machine provides an indexing mechanism to bring successive teeth into proper alignment with the grinding disc. This mechanism is operated by direct operation of the sharpening machine. The indexing operation, however, does not rely upon a sawtooth indexing pattern and pawl arrangement as is disclosed in the present application.
U.S. Pat. No. 535,496 to Hall discloses a relatively complex saw sharpening machine. Like the Fleck device, the Hall sharpening machine utilizes a tooth shape forming template or block that is utilized to control movement of the grinding wheel over the tooth configuration to produce a proper tooth shape. However, both devices depend on planar reciprocating motion of the grinding wheel to define the tooth faces. Further, neither Hall nor Fleck disclose an indexing mechanism that is easily adapted to all different sizes and numbers of blade teeth.
U.S. Pat. No. 1,551,230 discloses a hand-operated circular saw sharpened and gumming apparatus. Basically, it comprises a mounting device for a saw rather than a complete sharpening apparatus. The device mounts the saw on a vertically and horizontally movable carriage. The carriage is also mounted for rotation about a vertical axis to facilitate angular positioning of the saw blade for producing beveled surfaces. No device is disclosed for properly indexing the saw blade in precise increments about the axis of the arbor to establish the correct tooth spacing. Further, no device is illustrated or described for producing the proper tooth configuration moving the grinding disc in response to movement of a tracing pin along a tooth-shaped template.
U.S. Pat. No. 2,175,514 to Buchanan discloses a complex saw grinding machine that is utilized for grinding and sharpening of tubular saws with differing numbers of teeth and varying tube diameters. The arbor utilized to hold the tubular saws is indexed in increments corresponding to the number of sawteeth by operation of a selected ratchet wheel and pawl. The depth of the cut is determined by a cam arrangement and the tooth configuration is determined by the particular configuration of the grinding disc. The disc is automatically moved in a vertical plane to engage and sharpen each tooth at the end of a tube. As the grinding disc is raised away from engagement with the tube, the ratchet mechanism is operated to rotate the tube about a vertical axis, moving the next adjacent tooth into alignment with the grinding disc.
Of the above Patents, none describes the combination of (a) a tooth indexing mechanism whereby the sawteeth are accurately moved in prescribed angular increments about the axis of an arbor to locate the teeth in proper alignment with the grinding disc, and (b) a sawtooth template and trace pin whereby the proper configuration of an individual tooth may be formed by moving the trace pin over the sawtooth configuraion to impart identical movement of the grinding disc over the blade to be sharpened. The selected sawtooth template includes the back side, gullet, and face configuration desirable for the particular style of blade to be sharpened. In addition, few of the above described machines allow for the sharpening of a circular saw blade while jointing and gumming the blade in the same process.